Cobra 139XLR weak TX on certain channels
Cobra 139XLR weak TX on certain channels
This Cobra dead keys at about 4 watts on the upper 20 channels but below channel 20 it starts to drop in output watts all the way down to about <1watt on channel one. Also the channel indicator does not light up completely. I suspect it may be a problem with the uPD858c PLL How do you test the PLL chip? You out there Rick?
Re: Cobra 139XLR weak TX on certain channels.
The first think to do is re-alignment of the PLL and TX. Let us know how you get on.
Channel display could be just cold solder joints or it needs a new LED display.
Channel display could be just cold solder joints or it needs a new LED display.
Rick.
Heres what I did. I checked all channels with Dosy frequency counter and watt meter. 6 or 7 channels were off frequency I re-soldered the joints at the channel switch and rechecked the frequencies. They are all right on now. Heres the crazy thing - The watt meter is lowest on channel 1 at less than 1 watt. As I go up on the channels the watt meter comes up also. With channel 40 being the highest at just under 4 watts. And the watts come up evenly with each channel increase. What do you think Rick?
I can't do an alignment because I have no service manual (again)
I can't do an alignment because I have no service manual (again)
Re: Cobra 139XLR weak TX on certain channels.
The TX strip is easy to tune-up. Set the radio to channel 20 on AM with your power meter and dummy load, adjust the coils like so L30, L35, L36 for max power, then go to channel 1 and see what power is like, then channel 40 and see what power is like, you may need to adjust L30, L39 and L37 to balance the power from channel 1 and 40.
Rick.